Earlier devices, such as disclosed in International patent publication WO 94/23159, employ counter-rotating brushes. However, they can be used only to clean the sides of a pool at water level. Consequently, the pool must be drained to clean the complete side walls thereof. Furthermore, means to filter the dirty water are not available.
Another device is disclosed in German patent publication 1,920,172 and can be used only to clean the bottom of a pool. Although this device is equipped with a pump and a filter for cleaning the dirty water, it is not equipped with cleaning brushes of any kind.
Still another device is disclosed in U.S. Pat. No. 2,988,762 and is intended only for cleaning the bottom of a pool. This device is equipped with a pump and filter as well as fixed brushes which act on the already suction-cleaned surface and is, furthermore, provided at each end with adjustable bumpers which, on contact with the side of the pool, turns the device to the extent that it moves in a zigzag pattern over the bottom of the pool when returning in the opposite direction.